JP, A, 2006-103654 describes an airbag for restraining an occupant in the event of a vehicle collision or the like, in which a concave portion is formed in the vertical direction on the airbag surface facing the occupant in an inflated state. Paragraph 0039 of the above prior art discloses that, in the event of a frontal collision, the shoulder portion of the occupant is restrained by a shoulder restraining portion located on both sides of the above-described concave portion of the inflated airbag, causing the head portion of the occupant to be restrained as it enters the concave portion.
In the above-described airbag of prior art, the left-side shoulder restraining portion and the right-side shoulder restraining portion communicate with each other via a large hole close to the size of a longitudinal plane of the shoulder restraining portions in the front-back direction.
Further, in this airbag, as shown in FIG. 4, the depth of the concave portion is shallowest in the vertical intermediate part, and gradually deepens upward and downward from this intermediate part.